Brown, 22, hurt the knee cap on his right leg while recuperating from a reconstruction of his left knee.
In a statement on collingwoodfc.com.au, the Magpies said the emerging defender would undergo "a significant rest and rehabilitation period" before recommencing training for the 2012 pre-season.
Collingwood sports science director David Buttifant told media at Melbourne Airport on Saturday that the injury was the result a fall when he was walking.
"It could have easily happened back home at training. He has had a bit of a setback but his ACL (on his previously injured left knee) is coming on extremely well," he said.
Before the accident in the US, Brown, who shone in his two grand final appearances opposed to star St Kilda forward Nick Riewoldt, held some hope of returning to the Magpies' line-up before the end of the season.
"I want to get in there and hopefully he (coach Mick Malthouse) shows me the faith to put me back in and then I can repay him and do everything I can to get him another flag," the 195cm, 101kg defender said in an interview with the Herald Sun early this month.
Brown was one of four Magpies who flew to Arizona for Collingwood's mid-year altitude training camp, alongside Dane Swan, Darren Jolly and Brent Macaffer.
The Magpies travel to take on the Sydney Swans at ANZ Stadium on Saturday night.
